Porous sheet product and methods for making and using the same

Abstract

Porous sheet product and methods of making and using the same. In one embodiment, the porous sheet product may be made by a process that includes providing an extrusion mixture, the extrusion mixture including a polymeric binder, a swelling agent, a compatibilizing agent, and a superabsorbent polymer, the superabsorbent polymer being in particle form. The superabsorbent polymer may be wet-milled such that its particle size before and after milling is reduced by a ratio of at least 5:1. The extrusion mixture may be melt-extruded to form a sheet material in film form. At least a portion of the swelling and compatibilizing agents may be removed. The porous sheet product is preferably liquid permeable and may be used, for example, as a battery separator, as a food packaging material, as a diffusion barrier and disposable garments.

1 . A porous sheet product made by a method comprising (i) providing an extrusion mixture, the extrusion mixture comprising a polymeric binder and a superabsorbent polymer, the superabsorbent polymer being in particle form and having a particle size; (ii) milling the superabsorbent polymer such that the particle size of the superabsorbent polymer, before and after milling, is reduced by a ratio of at least 5:1, (iii) melt-extruding the extrusion mixture to form a sheet material in film form; and (iv) cooling the sheet material. 
     
     
         2 . The porous sheet product as claimed in  claim 1  wherein the milling step is performed before the melt-extruding step. 
     
     
         3 . The porous sheet product as claimed in  claim 1  wherein the milling step is performed concurrently with the melt-extruding step. 
     
     
         4 . The porous sheet product as claimed in  claim 1  wherein the milling step is performed while the superabsorbent polymer is present in the extrusion mixture. 
     
     
         5 . The porous sheet product as claimed in  claim 1  wherein the milling step is performed prior to providing the extrusion mixture. 
     
     
         6 . The porous sheet product as claimed in  claim 1  wherein the polymeric binder comprises a thermoplastic polymer, the thermoplastic polymer forming an open-celled matrix in the porous sheet product. 
     
     
         7 . The porous sheet product as claimed in  claim 6  wherein the thermoplastic polymer comprises at least one member selected from the group consisting of polyolefins, fluoropolymers, polyamides, polyethylene terephthalate, polyacrylics, polyvinyl acetate, polyvinyl alcohol, cellulosics, hydroxypropyl cellulose, polyacrylonitrile, polystyrene, polyurethane, polycarbonate, polysulfone, and polyimide. 
     
     
         8 . The porous sheet product as claimed in  claim 6  wherein the thermoplastic polymer comprises at least one member selected from the group consisting of elastomers of polyamide, polyolefin, polyether, polyisobutylene, polybutadiene, polystyrene, atactic polypropylene, polyurethane, ethylene-propylene rubber, ethylene-vinyl acetate copolymer, polyvinyl chloride, oxidized polyethylene, coumarone-indene resins, and terpene resins. 
     
     
         9 . The porous sheet product as claimed in  claim 6  wherein the thermoplastic polymer constitutes about 1-80% by volume of the extrusion mixture. 
     
     
         10 . The porous sheet product as claimed in  claim 1  wherein the superabsorbent polymer comprises at least one member selected from the group consisting of cross-linked polyacrylates, acrylic acid polymers, methacrylates, polyacrylamides, carboxymethyl celluloses, polyvinyl alcohol copolymers, polyethylene oxides, cellulose, starch-grafted copolyacrylates or polyacrylamides, ethylene maleic anhydride copolymers, and copolymers thereof. 
     
     
         11 . The porous sheet product as claimed in  claim 1  wherein the superabsorbent polymer has an initial, un-milled, dry size of about 20 microns to 5 mm. 
     
     
         12 . The porous sheet product as claimed in  claim 1  wherein the superabsorbent polymer, prior to swelling or milling, is added to the extrusion mixture and constitutes about 0.1-40% by volume of the extrusion mixture. 
     
     
         13 . The porous sheet product as claimed in  claim 1  wherein the milling step comprises wet-milling the superabsorbent polymer. 
     
     
         14 . The porous sheet product as claimed in  claim 13  wherein the method further comprises, prior to the milling step, swelling the superabsorbent polymer. 
     
     
         15 . The porous sheet product as claimed in  claim 14  wherein the superabsorbent polymer, after swelling, is at least twice as large in any of length, width, and height dimensions as the superabsorbent polymer, prior to swelling. 
     
     
         16 . The porous sheet product as claimed in  claim 14  wherein the swelling step comprises exposing the superabsorbent polymer to a swelling agent, whereby the superabsorbent polymer absorbs at least a portion of the swelling agent. 
     
     
         17 . The porous sheet product as claimed in  claim 16  wherein the swelling agent comprises at least one of water and a C1 to C3 alcohol or diol. 
     
     
         18 . The porous sheet product as claimed in  claim 16  wherein the method further comprises, after forming the sheet material, removing at least a portion of the swelling agent from the sheet material. 
     
     
         19 . The porous sheet product as claimed in  claim 16  wherein the swelling step further comprises exposing the superabsorbent polymer to an infused agent, whereby the superabsorbent polymer absorbs at least a portion of the infused agent. 
     
     
         20 . The porous sheet product as claimed in  claim 19  wherein the infused agent is at least one member selected from the group consisting of humectants, antistatic additives, ionic conductivity additives, color additives, flavorings, medications, and indicators. 
     
     
         21 . The porous sheet product as claimed in  claim 19  wherein the infused agent is present in an amount constituting about 0.1 to 60% by volume of the porous sheet product. 
     
     
         22 . The porous sheet product as claimed in  claim 19  wherein the method further comprises, after forming the sheet material, removing at least a portion of the swelling agent and/or the infused agent from the sheet material. 
     
     
         23 . The porous sheet product as claimed in  claim 1  wherein the extrusion mixture further comprises a compatibilizing agent that promotes uniform mixing of the polymeric binder and the superabsorbent polymer at extrusion temperature. 
     
     
         24 . The porous sheet product as claimed in  claim 23  wherein the compatibilizing agent constitutes about 1-80% by volume of the extrusion mixture. 
     
     
         25 . The porous sheet product as claimed in  claim 23  wherein the method further comprises, after forming the sheet material, removing at least a portion of the compatibilizing agent from the sheet material. 
     
     
         26 . The porous sheet product as claimed in  claim 1  wherein the extrusion mixture further comprises an inorganic oxide. 
     
     
         27 . The porous sheet product as claimed in  claim 1  wherein the porous sheet product consists of a single layer. 
     
     
         28 . The porous sheet product as claimed in  claim 1  wherein the porous sheet product comprises a plurality of layers. 
     
     
         29 . The porous sheet product as claimed in  claim 1  wherein the porous sheet product has a thickness of about 0.1-80 mils. 
     
     
         30 . A method of producing a porous sheet product, the method comprising the steps of:
 (a) providing an extrusion mixture, the extrusion mixture comprising a polymeric binder and a superabsorbent polymer, the superabsorbent polymer being in particle form and having a particle size;   (b) milling the superabsorbent polymer such that the particle size of the superabsorbent polymer before and after milling is reduced by a ratio of at least 5:1,   (c) melt-extruding the extrusion mixture to form a sheet material in film form; and   (d) cooling the sheet material.   
     
     
         31 . The method as claimed in  claim 30  wherein the milling step is performed before the melt-extruding step. 
     
     
         32 . The method as claimed in  claim 30  wherein the milling step is performed concurrently with the melt-extruding step. 
     
     
         33 . The method as claimed in  claim 30  wherein the milling step is performed while the superabsorbent polymer is present in the extrusion mixture. 
     
     
         34 . The method as claimed in  claim 30  wherein the milling step is performed prior to providing the extrusion mixture. 
     
     
         35 . The method as claimed in  claim 30  wherein the milling step is a wet-milling step, the method further comprising swelling the superabsorbent polymer with a liquid swelling agent. 
     
     
         36 . (canceled) 
     
     
         37 . A porous sheet product made by a method comprising (i) wet-milling a first mixture, the first mixture comprising a superabsorbent polymer, a swelling agent, and an infused agent, wherein the superabsorbent polymer is in particle form and has interstices, wherein the swelling agent and the infused agent form a one-phase homogeneous solution that is absorbed into the interstices of the superabsorbent polymer, wherein the wet-milling is such that the particle size of the superabsorbent polymer, before and after wet-milling, is reduced by a ratio of at least 5:1; (ii) melt-extruding a second mixture to form a sheet material in film form, the second mixture comprising the first mixture and a polymeric binder; and (iii) cooling the sheet material. 
     
     
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